Internet Architecture
Lecture 6:
How Routers Work
&
Connecting to the Internet
Assistant Teacher Samraa Adnan Al-Asadi
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How Routers Work
1* A router has input ports for receiving IP packets and
output ports for sending those packets toward their
destinations. When a packet comes to an input port, the
router examines the packet header and checks the
destination in it against a routing table a database that
tells the router how to send packets to various
destinations.
Assistant Teacher Samraa Adnan Al-Asadi
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How Routers Work
Assistant Teacher Samraa Adnan Al-Asadi
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How Routers Work
Assistant Teacher Samraa Adnan Al-Asadi
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How Routers Work
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How Routers Work
Assistant Teacher Samraa Adnan Al-Asadi
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How Routers Work
Assistant Teacher Samraa Adnan Al-Asadi
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Connecting to the Internet
You can connect to the Internet in many ways and many more ways pop
up practically every day. They range from simple telephone dial-in connections
to high-speed cable and digital subscriber lines (DSL) to satellite connections,
TV connections, wireless connections, connections at work and home via local
area networks (LANs), and even connections via cellular telephones.
One general rule is true about Internet connections: the faster, the better.
People want the fastest connection possible because many pictures, sounds, and
videos are available on the Internet. Today, the three most common ways you can
connect to the Internet are through a corporate or university LAN, at home via a
cable modem or DSL modem, or over telephone lines. Increasingly important,
though, are wireless connections via the WiFi networking standard. Direct
connections over LANs are generally the fastest connection, cable modems and
DSL modems are the second fastest, and telephone-line connections the slowest.
Cable modems, DSL modems, and LAN connections are all very high-speed
connections, and are known as broadband connections.
Assistant Teacher Samraa Adnan Al-Asadi
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Connecting to the Internet
At one time, most people connected to the Internet via dial-up modem.
Typically, when you use your modem to connect to the Internet, you dial in to an
Internet service provider (ISP). When you dial in to and connect to your ISP,
you're in fact connecting to a modem attached to a more powerful computer
called a server. ISPs typically have banks of hundreds or thousands of modems
that accept dial-ins from subscribers trying to connect. Modems are controlled by
your computer and communications software by a set of commands called the AT
command set (also known as the Hayes command set, named after one of the
original modem manufacturers, Hayes). It's a language that instructs the modem
on what to do at various points during a communications session, such as
opening up a line and sending out tones that the telephone system can
understand.
But there's a major problem with connecting this way it's too slow to be
of much use. Websites use many graphics and multimedia features, and dial-up
connections are so slow that the Web can seem unusable.
Assistant Teacher Samraa Adnan Al-Asadi
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Connecting to the Internet
Much faster than dial-up are so-called broadband connections. A
broadband connection is a generic name for a high-speed connection to the
Internet, most notably cable modems and Digital Subscriber Line (DSL)
connections.
Several types of DSL technologies are available, but they all work on
the same principles. They enable you to use your existing telephone lines to
access the Internet at very high speeds.
DSL technologies require that DSL modems be used on each end of the
phone line. In fact, the term DSL doesn't really refer to a phone line because an
ordinary, existing copper phone line can be used for DSL. Instead, it refers to the
DSL modems themselves. More confusing still, DSL modems aren't really
traditional modems at all. They don't attach to a serial port, as do traditional
modems. And they don't dial your telephone, as do traditional modems. Instead,
they connect to your computer via a much higher-speed port, either an Ethernet
port or a USB port, and they maintain an always-on connection over your phone
line. So, you always have an Internet connection when they are plugged into
your PC and turned on.
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
DSL technology has one drawback; it requires that your
house (and DSL modem) be located within a certain distance
from the telephone company office and its DSL modem. In
cities, this should not be a major problem, but it could be a
problem in rural areas. The exact distance required depends
on the type and speed of DSL service you use. Higher
speeds require that you be closer to the phone company
office.
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
1* Dumb
terminal: A terminal connected to a mainframe,
minicomputer, or other kind of large computer. This type of
connection often can be found in libraries or universities, although
those institutions are moving toward offering fuller Internet access
than dumb terminals provide.
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
Assistant Teacher Samraa Adnan Al-Asadi
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How Computers Connect to the
Internet
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Thank you
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